REPUBLICAN candidate Donald Trump has refused to rule out using nuclear weapons against ISIS and added America needs unpredictability following the Brussels terror attack.

Trump refused to rule nuclear weapons out during the Bloomberg interview

Speaking during an interview with Bloomberg after the massacre that killed 34 people, Trump confirmed he would not rule out any tactics such as the use of nuclear weapons in the fight against terrorism.

Calling for the need for unpredictability, he added that regardless of whether he would be willing to use the controversial weapons he wants ISIS to "think maybe we would use them".

But he also said he didn't want to talk at length about his thoughts because "the enemy is watching".

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Trump has called for the need for unpredicatability in the fight against ISIS

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But he also refused to say anymore in case the "enemies" were listening

The comments are likely to spark a huge debate as Hilary Clinton calls for the need for "steady hands" to fight against terrorism, implying her Presidential rival could not be trusted with America's arsenal.

Trump said: "I'm never going to rule anything out - I wouldn't want to say. Even if I wasn't, I wouldn't want to tell you that because at a minimum, I want them to think maybe we would use them.

"We need unpredictability. We don't know who these people are. The fact is, we need unpredictability and when you ask a question like that, it's a very sad thing to have to answer it.

Tributes for the Brussels attack victims began pouring in as soon as news of the devastating attack spread globally

"The enemy is watching and I have a very good chance of winning and I frankly don't want the enemy to know how I'm thinking.

"But with that being said, I don't rule out anything."

Trump has come under fire for his comments on Muslims in general.

He told fans they "do not respect us", adding that part of winning the fight against extremism is to "get them to respect the West and us".

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Police have confirmed so far 34 have lost their lives due to the attack

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Police searching people outside a rail station

The Republican candidate has previously announced his plans to bring back interrogation techniques such as water boarding along with changing the law to allow detainees to be tortured for information.

Trump has also spoken of "going after the families" of people who leave to fight for ISIS and has complained about international treaties that stop US troops from using the same tactics as ISIS on the battlefield.

He has also called for a ban on all Muslims from entering the country and increased surveillance on those already living and working in America.